Processes for improving the efficiency of hydrocarbon production

ABSTRACT

A process for converting a feed stream having carbon to C 2  to C 5  olefins, includes introducing a feed stream including methane and oxygen to a first reaction zone, reacting the methane and oxygen in the first reaction zone to form a first reaction zone product stream having a mixture of C 2  to C 5  alkanes, transporting the mixture of C 2  to C 5  alkanes to a second reaction zone, introducing a fresh stream of at least one of ethane and propane to the second reaction zone, converting the C 2  to C 5  alkanes to C 2  to C 5  olefins in the second reaction zone, producing one or more product streams in the second reaction zone, where a sum of the one or more product streams includes C 2  to C 5  olefins, and producing a recycle stream comprising hydrogen in the second reaction zone, where the recycle stream is transported to the first reaction zone.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a National Stage Entry under 35 U.S.C. 071 ofInternational Patent Application No. PCT/US2018/054954, filed Oct. 9,2018, which claims priority to U.S. Provisional Patent Application Ser.No. 62/570,325 filed Oct. 10, 2017, both of which are incorporated byreference herein their entirety.

This application claims priority to U.S. Provisional Patent ApplicationSer. No. 62/570,325 filed Oct. 10, 2017, which is incorporated byreference herein its entirety.

BACKGROUND Field

The present specification generally relates to processes and systems forconverting feed carbon to desired products while minimizing theconversion of the feed carbon to carbon dioxide (CO₂). In particular,the present specification relates to processes that use a hybridcatalyst and recycled hydrogen (H₂) to achieve a high conversion ofcarbon contained in a synthesis gas feed stream, to desired productswhile minimizing the conversion of the feed carbon to CO₂.

Technical Background

For a number of industrial applications, a desirable starting materialis a lower hydrocarbon—including, in particular, C₂ to C₅ olefins,and/or C₂ to C₅ paraffins that can then be converted to olefins—for usein or as starting materials to produce plastics, fuels, and variousdownstream chemicals. These C₂ to C₅ materials may be saturated orunsaturated and therefore may include ethane, ethylene, propane,propylene, butane, butylene, pentane, and/or pentylene. A variety ofprocesses of producing these lower hydrocarbons has been developed,including petroleum cracking and various synthetic processes.

Synthetic processes for converting feed carbon to desired products, suchas hydrocarbons, are known. Some of these synthetic processes begin withuse of a hybrid catalyst. Different types of catalysts have also beenexplored, as well as different kinds of feed streams and proportions offeed stream components. However, many of these synthetic processes havelow carbon conversion and much of the feed carbon does not get convertedand exits the process in the same form as the feed carbon, or the feedcarbon is converted to CO₂.

Accordingly, a need exists for processes that have a high conversion offeed carbon to desired products, such as, for example, C₂ to C₅hydrocarbons.

SUMMARY

According to one embodiment, a process for converting a feed streamhaving carbon to C₂ to C₅ olefins, comprises: introducing a feed streamcomprising methane and oxygen to a first reaction zone; reacting themethane and oxygen in the first reaction zone to form a first reactionzone product stream comprising a mixture of C₂ to C₅ alkanes;transporting the mixture of C₂ to C₅ alkanes to a second reaction zone;introducing a fresh stream of at least one of ethane and propane to thesecond reaction zone; converting the mixture of C₂ to C₅ alkanes to C₂to C₅ olefins in the second reaction zone; producing one or more productstreams in the second reaction zone, wherein a sum of the one or moreproduct streams comprises C₂ to C₅ olefins; and producing a recyclestream comprising hydrogen in the second reaction zone, wherein therecycle stream is transported to the first reaction zone.

In one or more embodiments, the second reaction zone comprises acracker, and a fresh stream of ethane is introduced into the cracker.

In some embodiments, the second reaction zone comprises a cracker and apropane dehydrogenation reactor, and a fresh stream of propane isintroduced into the propane dehydrogenation reactor.

In still other embodiments, the second reaction zone comprises a crackerand a propane dehydrogenation reactor. A fresh stream of ethane isintroduced into the cracker and a fresh stream of propane is introducedinto the propane dehydrogenation reactor.

Additional features and advantages will be set forth in the detaileddescription which follows, and in part will be readily apparent to thoseskilled in the art from that description or recognized by practicing theembodiments described herein, including the detailed description whichfollows, the claims, as well as the appended drawings.

It is to be understood that both the foregoing general description andthe following detailed description describe various embodiments and areintended to provide an overview or framework for understanding thenature and character of the claimed subject matter. The accompanyingdrawings are included to provide a further understanding of the variousembodiments, and are incorporated into and constitute a part of thisspecification. The drawings illustrate the various embodiments describedherein, and together with the description serve to explain theprinciples and operations of the claimed subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically depicts a first embodiment of a system and processfor converting a feed stream containing carbon to C₂ to C₅ olefinsaccording to embodiments disclosed and described herein;

FIG. 2A schematically depicts a second embodiment of a system andprocess for converting a feed stream containing carbon to C₂ to C₅olefins according to embodiments disclosed and described herein; and

FIG. 2B schematically depicts a third embodiment of a system and processfor converting a feed stream containing carbon to C₂ to C₅ olefinsaccording to embodiments disclosed and described herein.

DETAILED DESCRIPTION

Reference will now be made in detail to embodiments of processes forconverting a carbon-containing feed gas to a stream comprising C₂ to C₅hydrocarbons, such as, for example a stream comprising C₂ to C₅ olefins,embodiments of which are illustrated in the accompanying drawings.Whenever possible, the same reference numerals will be used throughoutthe drawings to refer to the same or like parts. In one embodiment, aprocess for converting a feed stream comprising carbon to C₂ to C₅olefins, comprises: introducing a feed stream comprising methane andoxygen to a first reaction zone; reacting the methane and oxygen in thefirst reaction zone to form a first reaction zone product streamcomprising a mixture of C₂ to C₅ alkanes; transporting the mixture of C₂to C₅ alkanes to a second reaction zone; introducing a fresh stream ofat least one of ethane and propane to the second reaction zone;converting the mixture of C₂ to C₅ alkanes to C₂ to C₅ olefins in thesecond reaction zone; producing a second reaction zone product streamcomprising H₂ and a mixture of C₂ to C₅ olefins; separating the secondreaction zone product stream into a product stream comprising C₂ to C₅olefins and recycle stream comprising H₂; and transporting the recyclestream to the first reaction zone.

With reference now to FIG. 1, an embodiment of system for converting afeed stream containing carbon to C₂ to C₅ hydrocarbons is provided. Itshould be understood that the embodiment depicted in FIG. 1 is exemplaryand does not limit the scope of this disclosure. As shown in theembodiment depicted in FIG. 1, a system 100 for converting a feed streamcontaining carbon to C₂ to C₅ hydrocarbons includes a first reactionzone 110, and a second reaction zone 130 that is fluidly connected tothe first reaction zone 110.

A process, according to one or more embodiments, for converting a feedstream containing carbon to C₂ to C₅ hydrocarbons using the system 100depicted in the embodiment of FIG. 1 will now be described. A feedstream 101 comprising methane (CH₄), oxygen (O₂), and, optionally, wateris introduced into the first reaction zone 110. It should be understoodthat the feed stream 101 may contain carbon sources other than methane,such as ethane, propane, butane, and low levels of CO₂ according tovarious embodiments.

The first reaction zone 110, according to embodiments, may comprise areformer (not shown) that uses water to convert the methane in the feedstream 101 to carbon monoxide (CO) and hydrogen in a conventional syngasgeneration process. For instance, according to one or more embodiments,the outlet of the reformer is at equilibrium for the followingreactions: (1) CH₄+H₂O→CO+3H₂; and (2) CO+H₂O→H₂+CO₂. Additionally,unreacted methane and water will be present at the outlet of thereformer. Although the temperature at which the reformer is operated isnot particularly limited so long as it can drive the above reactions, inone or more embodiments, the reformer is operated at an inlettemperature from greater than or equal to 400 degrees Celsius (° C.) toless than or equal to 450° C., such as from greater than or equal to415° C. to less than or equal to 435° C., or about 425° C. Likewise, thepressure at which the reformer is operated is not particularly limitedso long as it can drive the above reactions, in one or more embodiments,the reformer is operated at a pressure of greater than or equal to 38bar (3.8 MPa) to less than or equal to 46 bar (4.6 MPa), such as fromgreater than or equal to 40 bar (4.0 MPa) to less than or equal to 44bar (4.4 MPa), or about 42 bar (4.2 MPa). In embodiments, the feed intothe reformer may comprise from greater than or equal to 30 wt % methaneto less than or equal to 40 wt % methane, such as from greater than orequal to 33 wt % methane to less than or equal to 38 wt % methane, orabout 36 wt % methane. Accordingly, in embodiments, the feed into thereformer may comprise from greater than or equal to 60 wt % water toless than or equal to 70 wt % water, such as from greater than or equalto 62 wt % water to less than or equal to 67 wt % water, or about 63 wt% water.

Once the methane and water are converted into carbon monoxide andhydrogen (i.e., syngas) as disclosed above, the outlet stream of thereformer is introduced into a partial oxidation (PDX) reactor (notshown). In embodiments, the following reactions occur in the PDXreactor: (3) CH₄+0.5O₂→CO+2H₂; and (4) CH₄+2O₂→CO₂+2H₂O. In thesereactions, and according to embodiments, greater than or equal to 5 wt %to less than or equal to 15 wt % of the methane is converted to CO₂,such as greater than or equal to 7 wt % to less than or equal to 12 wt %of the methane is converted to CO₂, or about 10 wt % of the methane isconverted to CO₂. Accordingly, in embodiments, greater than or equal to85 wt % to less than or equal to 95 wt % of the methane is converted toCO, such as greater than or equal to 87 wt % to less than or equal to 92wt % of the methane is converted to CO, or about 90 wt % of the methaneis converted to CO. In embodiments, the outlet temperature of the PDXreactor may be from greater than or equal to 900° C. to less than orequal to 1100° C., such as from greater than or equal to 950° C. to lessthan or equal to 1050° C., or about 1000° C. Because the outlettemperature of the PDX reactor is higher than the reaction temperatureof the reformer, heat from the PDX reactor may be directed to thereformer to improve the energy efficiency of the first reaction zone110.

The outlet stream from the PDX reactor may then be introduced to ahybrid reactor where the outlet stream from the PDX reactor contacts ahybrid catalyst. The hybrid catalyst may, according to one or moreembodiments, include: (1) a methanol synthesis component; and (2) asolid microporous acid component having 8-MR access. In someembodiments, the methanol synthesis component is selected from the groupconsisting of a copper oxide catalyst, a copper oxide/zinc oxidecatalyst, a copper oxide/alumina catalyst, a copper oxide/zincoxide/alumina catalyst, a chromium oxide/zinc oxide catalyst, andcombinations thereof. In embodiments, the methanol synthesis componentmay comprise one or more of the elements Cu, Zn, Cr, and Al, in anypossible compositional combination and in either metallic or oxidicform. In embodiments, the solid microporous acid component is selectedfrom molecular sieves having 8-MR access and having a framework typeselected from the group consisting of the following framework types CHA,AEI, AFX, ERI, LTA, UFI, RTH, and combinations thereof, the frameworktypes corresponding to the naming convention of the InternationalZeolite Association. It should be understood that in embodiments, bothaluminosilicate and silicoaluminophosphate frameworks may be used. Incertain embodiments, the molecular sieve may be SAPO-34silicoaluminophosphate having a CHA framework type.

The use of hybrid catalysts to convert carbon-containing streams todesired products, such as, for example, C₂ to C₅ hydrocarbons, is known.In summary, hybrid catalysts closely couple sequential reactions on eachof the two independent catalysts. In the first step, a stream, such as,for example, syngas, is converted into oxygenated hydrocarbons (mostlymethanol and DME). In the second step, these oxygenates are convertedinto hydrocarbons (mostly short chain hydrocarbons, such as, for exampleC₂ to C₅ hydrocarbons). The continued withdrawal of oxygenates formed inthe first step by the reactions of the second step ensure that there isno thermodynamic limit to achieve close to 100% (>99.9%) feed carbonconversion to hydrocarbons.

Surprisingly, it has been found that known solutions in thesyngas-to-products field dealing with the formation of CO₂ are notdesirable for the hybrid catalyst system. In more genericsyngas-to-products processes, there are basically two options fordealing with the formation of CO₂; purging CO₂, or recycling CO₂ “toextinction” back to a syngas reformer section or over a catalyticreactor. The first option (purging) leads to a significant carbon yieldloss and is only feasible when the amount of CO₂ is very low, which isnot the case for the hybrid catalyst process. It has also been foundthat the second option (recycling CO₂) is not desirable for the hybridprocess for at least two reasons: it leads to a large and expensiveseparation section to separate CO₂ from the desired product; and itnegatively impacts the catalyst productivity.

In view of the above problems, there is presently no efficient way todeal with the loss of feed carbon to CO₂. To address these problems,embodiments of processes and systems disclosed herein recycle hydrogenfrom the downstream second reaction zone 130 to the first reaction zone110 to further drive the conversion of carbon in the feed stream 101 toC₂ to C₅ hydrocarbons. It should be understood that the systems andprocesses for converting carbon-containing streams to C₂ to C₅hydrocarbons disclosed herein are not required to use a hybrid catalystto convert carbon-containing streams to C₂ to C₅ hydrocarbons. However,according to some embodiments, the systems and processes for convertingcarbon-containing streams to C₂ to C₅ hydrocarbons disclosed herein areparticularly beneficial to processes using a hybrid catalyst.

The outlet stream from the PDX reactor is contacted with the hybridcatalyst under reaction conditions sufficient to form a first reactionzone product stream 120. The reaction conditions may comprise: atemperature ranging from greater than or equal to 300° C. to less thanor equal to 450° C., such as from greater than or equal to 350° C. toless than or equal to 430° C., or from greater than or equal to 360° C.to less than or equal to 420° C.; and a pressure of at least 1 bar (100kPa), such as at least 2 bar (200 kPa), or at least 3 bar (300 kPa). Inother embodiments, the pressure may at least 15 bar (1500 kPa), at least25 bar (2500 kPa), at least 30 bar (3000 kPa), at least 40 bar (4000kPa), or at least 50 bar (5000 kPa). The processes that occur in thefirst reaction zone 110 produce CO, CO₂, H₂, H₂O, CH₄ and C₂ to C₅hydrocarbons. In addition, inerts (such as, for example, nitrogen) thatare present in the feed stream will exit the first reaction zone as apurge stream. In embodiments these components may be separated andremoved from the first reaction zone in different streams. However, inembodiments, a light stream that comprises H₂, CO, CO₂, and CH₄ isrecycled and reused in the first reaction zone 110, such as bytransferring this light stream back to the reformer and the hybridreactor. The systems and methods for separating these streams are known,and any suitable separation can be conducted. Conventional separators,such as acid gas removal processes for CO₂, and simple condensation forwater removal, may be used. In embodiments, such as the embodimentdepicted in FIG. 1, at least four streams exit the first reaction zone110. A first exit stream 111 comprises, consists essentially of, orconsists of H₂O. A second exit stream 112 is a purge stream that purgesinert gases, such as, for example, nitrogen, from the first reactionzone. A third exit stream 113 comprises, consists essentially of, orconsists of CO₂. The final stream that exits the first reaction zone 110in the embodiment depicted in FIG. 1 is a first reaction zone productstream 120, which comprises C₂ to C₅ hydrocarbons. In one or moreembodiments, the C₂ to C₅ hydrocarbons comprise, consist essentially of,or consist of C₂ to C₅ alkanes. It should be understood that, inembodiments, the first reaction zone product stream 120 may comprise C₂to C₅ hydrocarbons other than C₂ to C₅ alkanes. In the embodimentdepicted in FIG. 1, the first reaction zone product stream 120 istransferred to the second reaction zone 130.

It should be understood that according to various embodiments, thecomponents of the first reaction zone, such as, for example, thereformer, the PDX reactor, and the reactor containing a hybrid catalyst,may be physically separate units or may be differentiated zones in asingle, physical unit. Embodiments include various combinations ofcomponents of the first reaction zone being physically separated orcombined in a single, physical unit. In addition, although specificreactions and processes for forming C₂ to C₅ hydrocarbons are disclosedabove as being a part of the first reaction zone 110, it should beunderstood that other processes for forming C₂ to C₅ hydrocarbons may beused in the first reaction zone 110 in addition to, or in place of, theprocesses disclosed above.

In the embodiment depicted in FIG. 1, the second reaction zone 130comprises a cracker. The first reaction zone product stream 120 entersthe second reaction zone 130 where at least a portion of the C₂ to C₅hydrocarbons—which comprise, consist essentially of, or consist of C₂ toC₅ alkanes—in the first reaction zone product stream 120 are convertedto C₂ to C₅ olefins, such as, for example, ethylene (C₂H₄), propylene(C₃H₆), and butylene (C₄H₈). Additional components that may be producedin the second reaction zone comprise H₂, CH₄, pyrolysis gas (pygas) andother heavy hydrocarbons, such as, for example, nonaromatic hydrocarbonsthat comprise more than five carbon atoms. It should also be understoodthat, in embodiments, not all the C₂ to C₅ alkanes in the first reactionzone product stream 120 will be converted to C₂ to C₅ olefins, and willremain as C₂ to C₅ alkanes. These unconverted C₂ to C₅ alkanes will exitthe cracker with the other components, but the C₂ to C₅ alkanes do notexit the second reaction zone 130 and can be recycled back to thecracker.

According to embodiments, a fresh stream of ethane 331 may be introducedinto the second reaction zone 130 in addition to first reaction zoneproduct stream 120. The first reaction zone product stream 120 and theethane in the fresh stream of ethane 331 may be converted into thesecond reaction zone product stream 132. The addition of the freshstream of ethane 331 provides, upon conversion in second reaction zone130, additional hydrogen that may be recycled back to the first reactionzone 110 as described in more detail below. In embodiments, any amountof ethane may be introduced into the second reaction zone 130. However,in various embodiments, the amount of the fresh stream of ethane 331 inthe total feed to the second reaction zone 130 (i.e., the first reactionzone product stream 120 plus the fresh stream of ethane 331) comprisesfrom greater than or equal to 5 wt % to less than or equal to 40 wt %,such as from greater than or equal to 10 wt % to less than or equal to35 wt %, or about 30 wt %. If too little fresh ethane is introduced intothe second reaction zone 130 via the fresh ethane stream 331, there willnot be a sufficient amount of H₂ recycled back to the first reactionzone 110 to provide a desired reduction of CO₂ produced in the firstreaction zone 110. However, if too much fresh ethane is introduced intothe second reaction zone via the fresh ethane stream 331, part of the H₂exiting the second reaction zone in the recycle stream 131 will need tobe purged as fuel to prevent the buildup of H₂, which creates aninefficiency in the conversion process. It should be understood that anyconventional steam cracker may be used in the second reaction zone 130so long as it is capable of converting the C₂ to C₅ hydrocarbons in thefirst reaction zone product stream 120—which comprises, consistsessentially of, or consists of C₂ to C₅ alkanes—combined with a freshstream of ethane 331, to a second reaction zone product stream 132 thatcomprises C₂ to C₅ olefins.

As discussed above, multiple components may exit the cracker, such as,for example, C₂ to C₅ alkanes, C₂ to C₅ olefins, H₂, CH₄, pyrolysis gas(pygas) and other heavy hydrocarbons. Thus, within the second reactionzone these various products may be separated and recycled, collected, ordiscarded. It should be understood that conventional separators, suchas, for example, cryogenic separators, may be used to separate thecomponents that exit the cracker in the second reaction zone 130. Forinstance, in the second reaction zone 130 at least three separations mayoccur: (1) C₂ to C₅ olefins may be separated from the components exitingthe cracker; (2) C₂ to C₅ alkanes may be separated from the componentsexiting the cracker, and (3) H₂ and, optionally, CH₄ may be separatedfrom the components that exit the cracker. Other components thatcomprise more than 5 carbon atoms may, in embodiments, be discarded fromthe second reaction zone 130 and used in other systems as desired.

Although not shown in FIG. 1, the C₂ to C₅ alkanes that exit the crackermay be recycled back to the cracker where they may be combined with theC₂ to C₅ alkanes that enter the cracker from the first reaction zoneproduct stream 120 and processed into C₂ to C₅ olefins. One stream thatexits the second reaction zone 130 is a recycle stream 131 thatcomprises, consists essentially of, or consists of H₂. In someembodiments, the recycle stream 131 comprises, consists essentially of,or consists of H₂ and CH₄. Another stream that exits the second reactionzone 130 is a product stream 132 that comprises, consists essentiallyof, or consists of C₂ to C₅ hydrocarbons—which comprise, consistessentially of, or consists of C₂ to C₅ olefins. The product stream 132is collected and used in various other processes to make end products.The recycle stream 131 is transferred from the second reaction zone 130to the first reaction zone 110. Thus, in some embodiments, H₂ isrecycled from second reaction zone 130 to the first reaction zone 110.In other embodiments, H₂ and CH₄ are recycled from the second reactionzone 130 to the first reaction zone 110. It should be understood thatthe amount of H₂ recycled back to the first reaction zone 110 in recyclestream 131 is determined by the amount of ethane added to the secondreaction zone 130.

By introducing a fresh ethane stream 331 into the second reaction zone130 and by recycling H₂ to the first reaction zone 110, certain massbalances may be achieved in the streams exiting the first reaction zone(i.e., the first exit stream 111, the second exit stream 112, the thirdexit stream 113, and the first reaction zone product stream 120) and inthe streams exiting the second reaction zone (i.e., the recycle stream131 and the product stream 132). The mass flow of the components presentin the streams exiting the first reaction zone, which is based on 1pound (lb.) of ethylene produced, includes from greater than or equal to0.085 lbs. to less than or equal to 0.095 lbs. pentane (C₅H₁₂), such asabout 0.088 lbs. C₅H₁₂; from greater than or equal to 0.170 lbs. to lessthan or equal to 0.185 lbs. butane (C₄H₁₀), such as about 0.177 lbs.C₄H₁₀; from greater than or equal to 0.500 lbs. to less than or equal to0.650 lbs. propane (C₃H₈), such as about 0.571 lbs. C₃H₈; from greaterthan or equal to 0.300 lbs. to less than or equal to 0.400 lbs. ethane(C₂H₆), such as about 0.342 lbs. C₂H₆; from greater than or equal to1.200 lbs. to less than or equal to 1.500 lbs. water (H₂O), such asabout 1.370 lbs. H₂O; and less than or equal to 0.010 lbs. CO₂, such asless than 0.005 lbs. CO₂, less than 0.001 lbs. CO₂, or even no CO₂.

In one or more embodiments, the mass flow of the components in thestreams exiting the second reaction zone, which is based on 1 lb. ofethylene produced, includes from greater than or equal to 0.0500 lbs. toless than or equal to 0.0700 lbs. H₂, such as about 0.0598 lbs. H₂; fromgreater than or equal to 0.1500 lbs. to less than or equal to 0.3500lbs. CH₄, such as about 0.2626 lbs. CH₄; about 1.0000 lbs. C₂H₄; fromgreater than or equal to 0.0500 lbs. to less than or equal to 0.2500lbs. C₃H₆, such as about 0.1598 lbs. C₃H₆; from greater than or equal to0.0750 lbs. to less than or equal to 0.0950 lbs. C₄H₈, such as about0.0854 lbs. C₄H₈; from greater than or equal to 0.0700 lbs. to less thanor equal to 0.0900 lbs. pygas, such as about 0.0813 lbs. pygas; and fromgreater than or equal to 0.0110 lbs. to less than or equal to 0.0130lbs. of other heavy hydrocarbons, such as about 0.0124 lbs. other heavyhydrocarbons.

With reference to the embodiment depicted in FIG. 2A, an embodiment ofsystem for converting a feed stream containing carbon to C₂ to C₅hydrocarbons is provided. It should be understood that the embodimentdepicted in FIG. 2A is exemplary and does not limit the scope of thisdisclosure. As shown in the embodiment depicted in FIG. 2A, a system 200for converting a feed stream containing carbon to C₂ to C₅ hydrocarbonsincludes a first reaction zone 110, and a second reaction zone 130—whichcomprises a cracker 210 and a propane dehydrogenation (PDH) reactor220—that is fluidly connected to the first reaction zone 110.

A process, according to one or more embodiments, for converting a feedstream containing carbon to C₂ to C₅ hydrocarbons using the system 200depicted in the embodiment of FIG. 2A will now be described. A feedstream 101 comprising methane (CH₄), oxygen (O₂), and, optionally, wateris introduced into the first reaction zone 110. It should be understoodthat the feed stream 101 may contain carbon sources other than methane,such as ethane, propane, butane, and low levels of CO₂ according tovarious embodiments.

The first reaction zone 110, according to embodiments, may comprise areformer (not shown) that uses water to convert the methane in the feedstream 101 to CO and H₂ in a conventional syngas generation process. Thereactions and reaction conditions of the reformer are provided abovewith reference to the embodiment depicted in FIG. 1.

Once the methane and water are converted into carbon monoxide andhydrogen (i.e., syngas), the outlet stream of the reformer is introducedinto a PDX reactor. The reactions and reaction conditions of the PDXreactor are provided above with reference to the embodiment depicted inFIG. 1. Because the outlet temperature of the PDX reactor is higher thanthe reaction temperature of the reformer, heat from the PDX reactor maybe directed to the reformer to improve the energy efficiency of thefirst reaction zone 110.

The outlet stream from the PDX reactor may then be introduced to ahybrid reactor where the outlet stream from the PDX reactor contacts ahybrid catalyst. The hybrid catalyst may, according to one or moreembodiments, include: (1) a methanol synthesis component; and (2) asolid microporous acid component having 8-MR access. In someembodiments, the methanol synthesis component is selected from the groupconsisting of a copper oxide catalyst, a copper oxide/zinc oxidecatalyst, a copper oxide/alumina catalyst, a copper oxide/zincoxide/alumina catalyst, a chromium oxide/zinc oxide catalyst, andcombinations thereof. In embodiments, the methanol synthesis componentmay comprise one or more of the elements Cu, Zn, Cr, and Al, in anypossible compositional combination and in either metallic or oxidicform. In embodiments, the solid microporous acid component is selectedfrom molecular sieves having 8-MR access and having a framework typeselected from the group consisting of the following framework types CHA,AEI, AFX, ERI, LTA, UFI, RTH, and combinations thereof, the frameworktypes corresponding to the naming convention of the InternationalZeolite Association. It should be understood that in embodiments, bothaluminosilicate and silicoaluminophosphate frameworks may be used. Incertain embodiments, the molecular sieve may be SAPO-34silicoaluminophosphate having a CHA framework type.

The processes that occur in the first reaction zone 110 produce CO, CO₂,H₂, H₂O, CH₄, and C₂ to C₅ hydrocarbons. In addition, inerts (such as,for example, nitrogen) that are present in the feed stream will exit thefirst reaction zone as a purge stream. In embodiments these componentsmay be separated and removed from the first reaction zone in differentstreams. However, in embodiments, a light stream that comprises H₂, CO,CO₂, and CH₄ is recycled and reused in the first reaction zone 110, suchas by transferring this light stream back to the reformer and the hybridreactor. The systems and methods for separating these streams are known,and any suitable separation can be conducted. Conventional separators,such as acid gas removal processes for CO₂, and simple condensation forwater removal, may be used. In embodiments, such as the embodimentdepicted in FIG. 2A, at least four streams exit the first reaction zone110. A first exit stream 111 comprises, consists essentially of, orconsists of H₂O. A second exit stream 112 is a purge stream that purgesinert gases, such as, for example, nitrogen, from the first reactionzone. A third exit stream 113 comprises, consists essentially of, orconsists of CO₂. The final stream that exits the first reaction zone 110in the embodiment depicted in FIG. 2A is a first reaction zone productstream 120, which comprises C₂ to C₅ hydrocarbons. In one or moreembodiments, the C₂ to C₅ hydrocarbons comprise, consist essentially of,or consist of C₂ to C₅ alkanes. It should be understood that, inembodiments, the first reaction zone product stream 120 may comprise C₂to C₅ hydrocarbons other than C₂ to C₅ alkanes. In the embodimentdepicted in FIG. 2A, the first reaction zone product stream 120 istransferred to the second reaction zone 130.

It should be understood that according to various embodiments, thecomponents of the first reaction zone 110, such as, for example, thereformer, the PDX reactor, and the reactor containing a hybrid catalyst,may be physically separate units or may be differentiated zones in asingle, physical unit. Embodiments include various combinations ofcomponents of the first reaction zone 110 being physically separated orcombined in a single, physical unit. In addition, although specificreactions and processes for forming C₂ to C₅ hydrocarbons are disclosedabove as being a part of the first reaction zone 110, it should beunderstood that other processes for forming C₂ to C₅ hydrocarbons may beused in the first reaction zone 110 in addition to, or in place of, theprocesses disclosed above.

In the embodiment depicted in FIG. 2A, the second reaction zone 130comprises a cracker 210 and a PDH reactor 220. The first reaction zoneproduct stream 120 enters the second reaction zone 130. In theembodiment depicted in FIG. 2A, the first reaction zone product stream120 is separated by a separator (not shown) in the second reaction zone130 into a first stream 123 comprising C₂, C₄, and C₅ hydrocarbons and asecond stream 124 comprising C₃ hydrocarbons. The first stream 123 isintroduced into the cracker 210 and the second stream 124 is introducedinto the PDH reactor 220. It should be understood that any conventionalseparator may be used to separate the first reaction zone product stream120 into the first stream 123 and the second stream 124.

In the cracker 210 C₂, C₄, and C₅ alkanes, which are present in thefirst stream 123, are reacted to form C₂, C₃, C₄, and C₅ olefins. Itshould be understood that any conventional cracker 210—such as thoseavailable for license from Technip, CB&I or other technology providers,also referred to a steam crackers, or cracking furnaces—may be used inthe second reaction zone 130 so long as it is capable of converting theC₂, C₄, and C₅ hydrocarbons in the first stream 123—which comprises,consists essentially of, or consists of C₂, C₄, and C₅ alkanes—to astream that comprises C₂, C₃, C₄, and C₅ olefins. Additional componentsthat may be produced in the cracker 210 comprise H₂, CH₄, pyrolysis gas(pygas) and other heavy hydrocarbons, such as, for example, nonaromatichydrocarbons that comprise more than five carbon atoms. It should alsobe understood that, in embodiments, not all the C₂, C₄, and C₅ alkanesin the first stream 123 will be converted to C₂, C₃, C₄, and C₅ olefins.Thus, unconverted C₂, C₄, and C₅ alkanes will exit the cracker with theother components. Although not shown in FIG. 2A, these unconverted C₂,C₄, and C₅ alkanes may be separated from the cracker output usingconventional separation techniques and equipment (not shown) andrecycled back to the cracker, such as, for example, by combining themwith the C₂, C₄, and C₅ alkanes in the first stream 123. In addition, H₂and CH₄ present in the cracker output may be separated from othercomponents of the cracker output using conventional separationtechniques and equipment (not shown) and recycled back to the firstreaction zone 110 in recycle stream 131. The C₂, C₃, C₄, and C₅ olefinsproduced in the cracker 210, may exit the second reaction zone 130 as aproduct stream 132 where it may be collected for use as a startingmaterial in other processes. Other components produced in the cracker210 may be separated using conventional techniques and equipment (notshown) as desired and discarded from the system 200. Additionally, anypropane may be separated from the streams exiting the cracker 210 andsent to the PDH reactor 220 in a propane-comprising stream 211.

According to embodiments, a fresh stream of ethane 331 may be introducedinto the cracker 210 in addition to the first stream 123. The C₂, C₄,and C₅ alkanes in the first stream 123 and the ethane in the freshstream of ethane 331 may be converted into C₂, C₃, C₄, and C₅ olefins.The addition of the fresh stream of ethane 331 provides, upon conversionin cracker 210, additional H₂ that may be recycled back to the firstreaction zone 110, as described in more detail below. In embodiments,any amount of ethane may be introduced into the second reaction zone130. However, in various embodiments, the amount of the fresh stream ofethane 331 in the total feed to the cracker 210 (i.e., the first stream123 plus the fresh ethane stream 331) comprises from greater than orequal to 5 wt % to less than or equal to 30 wt %, such as from greaterthan or equal to 10 wt % to less than or equal to 25 wt %, or about 17.5wt %. If too little fresh ethane is introduce into the cracker 210 viathe fresh ethane stream 331, there will not be a sufficient amount of H₂recycled back to the first reaction zone 110 to provide a desiredreduction of CO₂ produced in the first reaction zone 110. However, iftoo much fresh ethane is introduced into the cracker 210 via the freshethane stream 331, part of the H₂ exiting the cracker 210 will need tobe purged as fuel to prevent the buildup of H₂, which creates aninefficiency in the conversion process. It should be understood that anyconventional cracker 210—such as those available for license fromTechnip, CB&I or other technology providers, also referred to a steamcrackers, or cracking furnaces—may be used in the second reaction zone130 so long as it is capable of converting the C₂, C₄, and C₅hydrocarbons in the first stream 123—which comprises, consistsessentially of, or consists of C₂, C₄, and C₅ alkanes—combined with afresh stream of ethane 331, to a stream that comprises C₂, C₃, C₄, andC₅ olefins.

In the PDH reactor 220, C₃H₈, which is present in the second stream 124,is converted to C₃H₆. It should be understood that any conventional PDHreactor 220—such as, for example, UOP's Oleflex, CB&I Catofin, and UhdeSTAR—may be used in the second reaction zone 130 so long as it iscapable of converting the C₃H₈ in the second stream 124 to C₃H₆. Itshould be understood that, in embodiments, not all of the C₃H₈ thatenters the PDH reactor 220 will be converted to C₃H₆. Accordingly, thePDH reactor stream 221 that exits the PDH reactor 220 may comprise C₃H₆,C₃H₈, and one or more of H₂, CH₄, unreacted alkanes, and hydrocarbonscomprising more than 5 carbons.

The PDH reactor stream 221 is sent from the PDH reactor 220 to aseparation section of the cracker 210. Although not depicted in FIG. 2A,in embodiments, the cracker 210 includes a separation section thatseparates the various components formed in the cracker as well as thevarious components present in the PDH reactor stream 221. In theseparation section of the cracker 210, the C₃H₆ in the PDH reactorstream 221 will be separated from the PDH reactor stream 221 where itmay, in embodiments, be combined with the product stream 132 that exitsthe second reaction zone 130 and is collected for further use. Likewise,in embodiments, H₂ and, optionally, CH₄ that are present in the PDHreactor stream 221 may be separated from the PDH reactor stream 221 inthe separation section of the cracker 210 and combined with recyclestream 131, where it exits the second reaction zone 130 and is recycledby being sent to the first reaction zone 110. Unreacted alkanes in thePDH reactor stream 221 may, in one or more embodiments, be separatedfrom the PDH reactor stream 221 in the separation section of the cracker210 where the unreacted alkanes can be further processed by the cracker210 and converted into C₂ to C₅ olefins that can exit the secondreaction zone in product stream 132. However, any propane present in thePDH reactor stream 221 will, in embodiments, be returned to the PDHreactor 220 in a propane-comprising stream 211, where the propane may beprocessed by the PDH reactor and converted to C₃H₆. Any hydrocarbonscomprising more than 5 carbons present in the PDH reactor stream 221may, in some embodiments, be separated from the PDH reactor stream 221in the separation section of the cracker 210 and discarded from thesecond reaction zone 130 in a discard stream (not shown).

It should be understood that according to various embodiments, thecomponents of the second reaction zone 130, such as, for example, thecracker 210 (including the separation section of the cracker), and thePDH reactor 220, may be physically separate units or may bedifferentiated zones in a single, physical unit. Embodiments includevarious combinations of components of the second reaction zone 130 beingphysically separated or combined in a single, physical unit.

By introducing a fresh ethane stream 331 into the second reaction zone130 and by recycling H₂ to the first reaction zone 110, certain massbalances may be achieved in the streams exiting the first reaction zone(i.e., the first exit stream 111, the second exit stream 112, the thirdexit stream 113, and the first reaction zone product stream 120) and inthe streams exiting the second reaction zone (i.e., the recycle stream131 and the product stream 132. It should be understood that where morethan one product stream exits the second reaction zone 130, thecombination of all the product streams exiting the second reaction zone130 may be referred to as “a sum of the one or more product streams”. Inone or more embodiments, the mass flow of the components present in thestreams exiting the first reaction zone, which is based on 1 lb. ofethylene produced, includes from greater than or equal to 0.050 lbs. toless than or equal to 0.250 lbs. C₅H₁₂, such as about 0.152 lbs. C₅H₁₂;from greater than or equal to 0.200 lbs. to less than or equal to 0.400lbs. C₄H₁₀, such as about 0.304 lbs. C₄H₁₀; from greater than or equalto 0.850 lbs. to less than or equal to 1.050 lbs. C₃H₈, such as about0.984 lbs. C₃H₈; from greater than or equal to 0.450 lbs. to less thanor equal to 0.650 lbs. C₂H₆, such as about 0.588 lbs. C₂H₆; from greaterthan or equal to 2.200 lbs. to less than or equal to 2.500 lbs. H₂O,such as about 2.360 lbs. H₂O; and less than or equal to 0.010 lbs. CO₂,such as less than 0.005 lbs. CO₂, less than 0.001 lbs. CO₂, or even noCO₂.

In one or more embodiments, the mass flow of the components present inthe streams exiting the second reaction zone, which is based on 1 lb. ofethylene produced, includes from greater than or equal to 0.0900 lbs. toless than or equal to 0.1100 lbs. H₂, such as about 0.1036 lbs. H₂; fromgreater than or equal to 0.1900 lbs. to less than or equal to 0.2300lbs. CH₄, such as about 0.2106 lbs. CH₄; about 1.0000 lbs. C₂H₄; fromgreater than or equal to 0.8000 lbs. to less than or equal to 1.0000lbs. C₃H₆, such as about 0.9212 lbs. C₃H₆; from greater than or equal to0.0900 lbs. to less than or equal to 0.1100 lbs. C₄H₈, such as about0.0998 lbs. C₄H₈; from greater than or equal to 0.0700 lbs. to less thanor equal to 0.0900 lbs. pygas, such as about 0.0863 lbs. pygas; and fromgreater than or equal to 0.0120 lbs. to less than or equal to 0.0150lbs. of other heavy hydrocarbons, such as about 0.0139 lbs. other heavyhydrocarbons.

With reference to the embodiment depicted in FIG. 2B, an embodiment ofsystem for converting a feed stream containing carbon to C₂ to C₅hydrocarbons is provided. It should be understood that the embodimentdepicted in FIG. 2B is exemplary and does not limit the scope of thisdisclosure. As shown in the embodiment depicted in FIG. 2B, a system 200for converting a feed stream containing carbon to C₂ to C₅ hydrocarbonsincludes a first reaction zone 110, and a second reaction zone 130—whichcomprises a cracker 210 and a PDH reactor 220—that is fluidly connectedto the first reaction zone 110.

A process, according to one or more embodiments, for converting a feedstream containing carbon to C₂ to C₅ hydrocarbons using the system 200depicted in the embodiment of FIG. 2B will now be described. A feedstream 101 comprising methane (CH₄), oxygen (O₂), and, optionally, wateris introduced into the first reaction zone 110. It should be understoodthat the feed stream 101 may contain carbon sources other than methane,such as ethane, propane, butane, and low levels of CO₂ according tovarious embodiments.

The first reaction zone 110, according to embodiments, may comprise areformer (not shown) that uses water to convert the methane in the feedstream 101 to CO and H₂ in a conventional syngas generation process. Thereactions and reaction conditions of the reformer are provided abovewith reference to the embodiment depicted in FIG. 1.

Once the methane and water are converted into carbon monoxide andhydrogen (i.e., syngas), the outlet stream of the reformer is introducedinto a PDX reactor (not shown). The reactions and reaction conditions ofthe PDX reactor are provided above with reference to the embodimentdepicted in FIG. 1. Because the outlet temperature of the PDX reactor ishigher than the reaction temperature of the reformer, heat from the PDXreactor may be directed to the reformer to improve the energy efficiencyof the first reaction zone 110.

The outlet stream from the PDX reactor may then be introduced to ahybrid reactor where the outlet stream from the PDX reactor contacts ahybrid catalyst. The hybrid catalyst may, according to one or moreembodiments, include: (1) a methanol synthesis component; and (2) asolid microporous acid component having 8-MR access. In someembodiments, the methanol synthesis component is selected from the groupconsisting of a copper oxide catalyst, a copper oxide/zinc oxidecatalyst, a copper oxide/alumina catalyst, a copper oxide/zincoxide/alumina catalyst, a chromium oxide/zinc oxide catalyst, andcombinations thereof. In embodiments, the methanol synthesis componentmay comprise one or more of the elements Cu, Zn, Cr, and Al, in anypossible compositional combination and in either metallic or oxidicform. In embodiments, the solid microporous acid component is selectedfrom molecular sieves having 8-MR access and having a framework typeselected from the group consisting of the following framework types CHA,AEI, AFX, ERI, LTA, UFI, RTH, and combinations thereof, the frameworktypes corresponding to the naming convention of the InternationalZeolite Association. It should be understood that in embodiments, bothaluminosilicate and silicoaluminophosphate frameworks may be used. Incertain embodiments, the molecular sieve may be SAPO-34silicoaluminophosphate having a CHA framework type.

The processes that occur in the first reaction zone 110 produce CO, CO₂,H₂, H₂O, CH₄, and C₂ to C₅ hydrocarbons. In addition, inerts (such as,for example, nitrogen) that are present in the feed stream will exit thefirst reaction zone as a purge stream. In embodiments these componentsmay be separated and removed from the first reaction zone in differentstreams. However, in embodiments, a light stream that comprises H₂, CO,CO₂, and CH₄ is recycled and reused in reaction zone 110, such as bytransferring this light stream back to the reformer and the hybridreactor. The systems and methods for separating these streams are known,and any suitable separation can be conducted. Conventional separators,such as acid gas removal processes for CO₂, and simple condensation forwater removal, may be used. In embodiments, such as the embodimentdepicted in FIG. 2B, at least four streams exit the first reaction zone110. A first exit stream 111 comprises, consists essentially of, orconsists of H₂O. A second exit stream 112 is a purge stream that purgesinert gases, such as, for example, nitrogen, from the first reactionzone. A third exit stream 113 comprises, consists essentially of, orconsists of CO₂. The final stream that exits the first reaction zone 110in the embodiment depicted in FIG. 2B is a first reaction zone productstream 120, which comprises C₂ to C₅ hydrocarbons. In one or moreembodiments, the C₂ to C₅ hydrocarbons comprise, consist essentially of,or consist of C₂ to C₅ alkanes. It should be understood that, inembodiments, the first reaction zone product stream 120 may comprise C₂to C₅ hydrocarbons other than C₂ to C₅ alkanes. In the embodimentdepicted in FIG. 2B, the first reaction zone product stream 120 istransferred to the second reaction zone 130.

It should be understood that according to various embodiments, thecomponents of the first reaction zone, such as, for example, thereformer, the PDX reactor, and the reactor containing a hybrid catalyst,may be physically separate units or may be differentiated zones in asingle, physical unit. Embodiments include various combinations ofcomponents of the first reaction zone being physically separated orcombined in a single, physical unit. In addition, although specificreactions and processes for forming C₂ to C₅ hydrocarbons are disclosedabove as being a part of the first reaction zone 110, it should beunderstood that other processes for forming C₂ to C₅ hydrocarbons may beused in the first reaction zone 110 in addition to, or in place of, theprocesses disclosed above.

In the embodiment depicted in FIG. 2B, the second reaction zone 130comprises a cracker 210 and a PDH reactor 220. The first reaction zoneproduct stream 120 enters the second reaction zone 130. In theembodiment depicted in FIG. 2B, the first reaction zone product stream120 is separated by a separator (not shown) in the second reaction zone130 into a first stream 123 comprising C₂, C₄, and C₅ hydrocarbons and asecond stream 124 comprising C₃ hydrocarbons. The first stream 123 isintroduced into the cracker 210 and the second stream 124 is introducedinto the PDH reactor 220. It should be understood that any conventionalseparator may be used to separate the first reaction zone product stream120 into the first stream 123 and the second stream 124.

In the cracker 210 C₂, C₄, and C₅ alkanes, which are present in thefirst stream 123, are reacted to form C₂, C₃, C₄, and C₅ olefins. Itshould be understood that any conventional cracker 210—such as thoseavailable for license from Technip, CB&I or other technology providers,also referred to a steam crackers, or cracking furnaces—may be used inthe second reaction zone 130 so long as it is capable of converting theC₂, C₄, and C₅ hydrocarbons in the first stream 123—which comprises,consists essentially of, or consists of C₂, C₄, and C₅ alkanes—to astream that comprises C₂, C₃, C₄, and C₅ olefins. Additional componentsthat may be produced in the cracker 210 comprise H₂, CH₄, pyrolysis gas(pygas) and other heavy hydrocarbons, such as, for example, nonaromatichydrocarbons that comprise more than five carbon atoms. It should alsobe understood that, in embodiments, not all the C₂, C₄, and C₅ alkanesin the first stream 123 will be converted to C₂, C₃, C₄, and C₅ olefins.Thus, unconverted C₂, C₄, and C₅ alkanes will exit the cracker with theother components. Although not shown in FIG. 2B, these unconverted C₂,C₄, and C₅ alkanes may be separated from the cracker output usingconventional separation techniques and equipment (not shown) andrecycled back to the cracker, such as, for example, by combining themwith the C₂, C₄, and C₅ alkanes in the first stream 123. In addition, H₂and CH₄ present in the cracker output may be separated from othercomponents of the cracker output using conventional separationtechniques and equipment (not shown) and recycled back to the firstreaction zone 110 in recycle stream 131. The C₂, C₃, C₄, and C₅ olefinsproduced in the cracker 210, may exit the second reaction zone 130 as aproduct stream 132 where it may be collected for use as a startingmaterial in other processes. Other components produced in the cracker210 may be separated using conventional techniques and equipment (notshown) as desired and discarded from the system 200. Additionally, anypropane may be separated from the streams exiting the cracker 210 andsent to the PDH reactor 220 in a propane-comprising stream 211.

In the PDH reactor 220, C₃H₈, which is present in the second stream 124,is converted to C₃H₆. According to embodiments, a fresh stream ofpropane 332 may be introduced into the PDH reactor 220 in addition tothe second stream 124. The C₃H₈ in the second stream 124 and the propanein the fresh stream of propane 332 may be converted into C₃H₆. Theaddition of the fresh stream of propane 332 provides, upon conversion inPDH reactor 220, additional hydrogen that may be recycled back to thefirst reaction zone 110 as described in more detail below. Inembodiments, any amount of propane may be introduced into the secondreaction zone 130. However, in various embodiments, the amount of thefresh stream of propane 332 in the total feed to the PDH reactor 220(i.e., the second stream 124 plus the fresh propane stream 332)comprises from greater than or equal to 5 wt % to less than or equal to30 wt %, such as from greater than or equal to 10 wt % to less than orequal to 25 wt %, or about 22 wt %. If too little fresh propane isintroduce into the PDH reactor 220 via the fresh propane stream 332,there will not be a sufficient amount of H₂ recycled back to the firstreaction zone 110 to provide a desired reduction of CO₂ produced in thefirst reaction zone 110. However, if too much fresh propane isintroduced into the PDH reactor 220 via the fresh propane stream 332,part of the H₂ exiting the PDH reactor 220 will need to be purged asfuel to prevent the buildup of H₂, which creates an inefficiency in theconversion process. It should be understood that any conventional PDHreactor 220—such as, for example, UOP's Oleflex, CB&I Catofin, and UhdeSTAR—may be used in the second reaction zone 130 so long as it iscapable of converting the C₃H₈ in the second stream 124, combined with afresh stream of propane 332, to C₃H₆. It should be understood that, inembodiments, not all of the C₃H₈ that enters the PDH reactor 220 will beconverted to C₃H₆. Accordingly, the PDH reactor stream 221 that exitsthe PDH reactor 220 may comprise C₃H₆, C₃H₈, and one or more of H₂, CH₄,unreacted alkanes, and hydrocarbons comprising more than 5 carbons.

The PDH reactor stream 221 is sent from the PDH reactor 220 to aseparation section of the cracker 210. Although not depicted in FIG. 2B,in embodiments, the cracker 210 includes a separation section thatseparates the various components formed in the cracker as well as thevarious components present in the PDH reactor stream 221. In theseparation section of the cracker 210, the C₃H₆ in the PDH reactorstream 221 will be separated from the PDH reactor stream 221 where itmay, in embodiments, be combined with the product stream 132 that exitsthe second reaction zone 130 and is collected for further use. Likewise,in embodiments, H₂ and, optionally, CH₄ that are present in the PDHreactor stream 221 may be separated from the PDH reactor stream 221 inthe separation section of the cracker 210 and combined with recyclestream 131, where it exits the second reaction zone 130 and is recycledby being sent to the first reaction zone 110. Unreacted alkanes in thePDH reactor stream 221 may, in one or more embodiments, be separatedfrom the PDH reactor stream 221 in the separation section of the cracker210 where the unreacted alkanes can be further processed by the cracker210 and converted into C₂ to C₅ olefins that can exit the secondreaction zone in product stream 132. However, any propane present in thePDH reactor stream 221 will, in embodiments, be returned to the PDHreactor 220 in a propane-comprising stream 211, where the propane may beprocessed by the PDH reactor and converted to C₃H₆. Any hydrocarbonscomprising more than 5 carbons present in the PDH reactor stream 221may, in some embodiments, be separated from the PDH reactor stream 221in the separation section of the cracker 210 and discarded from thesecond reaction zone 130 in a discard stream (not shown).

It should be understood that according to various embodiments, thecomponents of the second reaction zone 130, such as, for example, thecracker 210 (including the separation section), and the PDH reactor 220,may be physically separate units or may be differentiated zones in asingle, physical unit. Embodiments include various combinations ofcomponents of the second reaction zone 130 being physically separated orcombined in a single, physical unit.

By introducing a fresh propane stream 332 into the second reaction zone130 and by recycling H₂ to the first reaction zone 110, certain massbalances may be achieved in the streams exiting the first reaction zone(i.e., the first exit stream 111, the second exit stream 112, the thirdexit stream 113, and the first reaction zone product stream 120) and inthe streams exiting the second reaction zone (i.e., the recycle stream131 and the product stream 132. It should be understood that where morethan one product stream exits the second reaction zone 130, thecombination of all the product streams exiting the second reaction zone130 may be referred to as “a sum of the one or more product streams”. Inone or more embodiments, the mass flow of the components present in thestreams exiting the first reaction zone, which is based on 1 lb. ofethylene produced, includes from greater than or equal to 0.100 lbs. toless than or equal to 0.300 lbs. C₅H₁₂, such as about 0.218 lbs. C₅H₁₂;from greater than or equal to 0.300 lbs. to less than or equal to 0.500lbs. C₄H₁₀, such as about 0.436 lbs. C₄H₁₀; from greater than or equalto 1.300 lbs. to less than or equal to 1.500 lbs. C₃H₈, such as about1.410 lbs. C₃H₈; from greater than or equal to 0.750 lbs. to less thanor equal to 0.950 lbs. C₂H₆, such as about 0.843 lbs. C₂H₆; from greaterthan or equal to 3.200 lbs. to less than or equal to 3.500 lbs. H₂O,such as about 3.386 lbs. H₂O; and less than or equal to 0.010 lbs. CO₂,such as less than 0.005 lbs. CO₂, less than 0.001 lbs. CO₂, or even noCO₂.

In one or more embodiments, the mass flow of the components present inthe streams exiting the second reaction zone, which is based on 1 lb. ofethylene produced, includes from greater than or equal to 0.1400 lbs. toless than or equal to 0.1600 lbs. H₂, such as about 0.1490 lbs. H₂; fromgreater than or equal to 0.2900 lbs. to less than or equal to 0.3100lbs. CH₄, such as about 0.2971 lbs. CH₄; about 1.0000 lbs. C₂H₄; fromgreater than or equal to 1.9000 lbs. to less than or equal to 2.1000lbs. C₃H₆, such as about 1.9900 lbs. C₃H₆; from greater than or equal to0.1200 lbs. to less than or equal to 0.1400 lbs. C₄H₈, such as about0.1317 lbs. C₄H₈; from greater than or equal to 0.1000 lbs. to less thanor equal to 0.1200 lbs. pygas, such as about 0.1134 lbs. pygas; and fromgreater than or equal to 0.0165 lbs. to less than or equal to 0.0185lbs. of other heavy hydrocarbons, such as about 0.0176 lbs. other heavyhydrocarbons.

It should be understood that in various embodiments: (1) fresh ethane(331) may be fed to the cracker in addition to the stream introduced tothe cracker from the first reaction zone and no fresh propane (332) maybe fed to the PDH reactor; (2) fresh propane (332) may be fed to the PDHreactor in addition to the stream introduced to the cracker from thefirst reaction zone and no fresh ethane (331) may be fed to the cracker;or (3) fresh ethane (331) may be fed to the cracker in addition to thestream introduced to the cracker from the first reaction zone and freshpropane (332) may be fed to the PDH reactor. Further, in someembodiments, propane (332) may be fed to the cracker alone, or propane(332) may be fed to both the cracker and the PDH reactor.

Embodiments of systems and processes for converting a stream comprisingcarbon into C₂ to C₅ hydrocarbons result in improved efficiencies overknown processes for converting a stream comprising carbon into C₂ to C₅hydrocarbons. For instance, in one or more embodiments, a ratio inlb./lb. of CH₄ fed to the system in a feed stream—including any recycledCH₄—and C₂ to C₅ alkanes produced (CH₄/alkanes ratio) is less than 1.17,such as less than or equal to 1.15, less than or equal to 1.14, lessthan or equal to 1.13, or less than or equal to 1.12. For each of theabove embodiments, the CH₄/alkanes ratio is greater than or equal to1.00, such as greater than or equal to 1.05, or greater than or equal to1.10.

Additionally, in some embodiments, a ratio in lb./lb. of O₂ fed to thesystem in a feed stream to C₂ to C₅ alkanes produced (O₂/alkanes ratio)is less than or equal to 1.10, such as less than or equal to 1.08, lessthan or equal to 1.06, less than or equal to 1.05, or less than or equalto 1.04. For each of the above embodiments, the O₂/alkanes ratio isgreater than or equal to 1.00, such as greater than or equal to 1.01, orgreater than or equal to 1.02.

Further, in various embodiments, the efficiency for converting carbon inCH₄ to C₂ to C₅ alkanes is greater than 0.93, such as greater than orequal to 0.94, greater than or equal to 0.95, greater than or equal to0.96, greater than or equal to 0.97, greater than or equal to 0.98, orgreater than or equal to 0.99.

EXAMPLES

Embodiments will be further clarified by the following examples. Themass balances in the examples provided below may be obtained by askilled artisan using conventional modelling software, such as, forexample, Aspen.

Syngas generation is required for the production of alkanes. The syngasgeneration process is the same for all cases with the same operatingassumptions. Syngas generation is accomplished by feeding methane andwater into a reformer. In cases that involve the recycle of methane andH₂, this feed will also contain H₂.

The feed to the reformer is at 425° C. and the composition if 36 wt %CH₄ and 63 wt % water. H₂ can also be fed into the reformer with themethane, and the temperature is also 425° C. The reformer pressure is 42bar.

The reformer outlet is at equilibrium for the following reactions:CH₄+H₂O═CO+3H₂  1)CO+H₂O═H₂+CO₂  2)

The outlet of the reformer is fed to a PDX with oxygen feed where thefollowing reactions occur:CH₄+0.5O₂═CO+2H₂  3)CH₄+2O₂═CO₂+2H₂O  4)

Ten percent of the methane that is reacted is assumed to be converted toCO₂ and 90 percent is converted to CO. The methane concentration at thePDX outlet is controlled to be 1.5 mol % by the oxygen feed rate. Theoutlet stream from the PDX supplies the heat to the reformer by beingcooled to 450° C. on the reformer shell. Water is removed from thesyngas before feeding the alkane production reaction.

Alkane products are produced in the following distribution:

relative moles/hr 3H₂ + CO = CH₄ + H₂O 12.1 5H₂ + 2CO = C₂H₆ + 2H₂O 34.47H₂ + 3CO = C₃H₈ + 3H₂O 40.4 9H₂ + 4CO = C₄H₁₀ + 4H₂O 9.4 11H₂ + 5CO =C₅H₁₂ + 5H₂O 3.7

The reactor product is also in water gas shift equilibrium.

Three reactor stages are used in the simulations. After each reactorstage, water is removed before feeding to the next reactor stage. The COconversion across all three reactor stages is specified to be 90%. Usingthree reactor stages in this manner is not essential for the invention:similar results would have been obtained using a single reactor at equalCO conversion level.

The product gas from the reactor is separated into a water stream, aproduct stream containing C₂H₆ and higher carbon products, and a gasstream containing H₂, N₂, CO, CO₂, and CH₄. Twenty five percent of thisstream is fed back to the reformer to control the CH₄ concentration atthe reactor inlet at about 6 mol %. About 8 mol % is purged to controlthe N₂ concentration at about 2 mol % at the reactor inlet. N₂ isassumed to enter the process in the CH₄ feed gas at 1 mol %. For theremaining gas, a portion of the CO₂ is removed and the remainder of thegas is recycled to the reactor. The CO₂ removal is used to control thereactor inlet concentration at about 12 mol % CO₂.

The alkane products are converted to olefins by conventional steamcracking, or a combination of steam cracking and propanedehydrogenation. The assumptions on cracking efficiency for each feedcomponent are given in Table 1 below:

TABLE 1 Feed component ethylene propylene C₄ pygas heavies fuel, CH₄fuel, H₂ C₂H₆ ethane 77.2 2.1 2.9 2.9 0.4 7.6 5.6 propane 44.1 16.6 4.35.1 0.6 26.3 1.7 butane 38.8 19.5 15.9 4.3 0.3 19.2 0.8 pentane 29.314.4 9.3 22.7 5.7 16.4 0.9 PDH 0.616 83.1 0.62 0.757 4.65 3.97 5.94Product composition from cracking in weight percent.

Example 1

Example 1 is a simulation of the conversion of a carbon-containingstream to C₂ to C₅ hydrocarbons according to embodiments depicted inFIG. 1. In particular, a feed stream comprising CH₄ and O₂ is fed to afirst reaction zone comprising an alkane production unit. The mass flowof the feed stream, based on the production of 1 lb. of ethylene, is1.076 lbs. CH₄ and 1.238 lbs. O₂.

The first reaction zone product stream comprises CO₂, H₂O, C₂H₆, C₃H₈,C₄H₁₀, and C₅H₁₂. The CO₂ and H₂O are separated from the remainingcomponents (i.e., C₂H₆, C₃H₈, C₄H₁₀, and C₅H₁₂) and discarded. The massflow of the first reaction zone product stream, based on the productionof 1 lb. of ethylene, is 0.005 lbs. CO₂, 1.370 lbs. H₂O, 0.342 lbs.C₂H₆, 0.571 lbs. C₃H₈, 0.177 lbs. C₄H₁₀, and 0.088 lbs. C₅H₁₂.

The C₂H₆, C₃H₈, C₄H₁₀, and C₅H₁₂ produced in the first reaction zone arefed along with a feed of additional fresh ethane to a second reactionzone comprising a conventional cracker, which produces C₂ to C₅ olefins.The fresh ethane makes up 30 wt % of the feed to the cracker. The massflow of the fresh ethane, based on the production of 1 lb. of ethylene,is 0.505 lbs.

The second reaction zone product stream comprises H₂, CH₄, C₂H₄, C₃H₆,C₄H₈, pygas, and other heavy hydrocarbons. The mass flow of the secondreaction zone product stream, based on the production of 1 lb. ofethylene, is 0.0598 lbs. H₂, 0.2626 lbs. CH₄, 1.0000 lbs. C₂H₄, 0.1598lbs. C₃H₆, 0.0854 lbs. C₄H₈, 0.0813 lbs. pygas, and 0.0124 lbs. of otherheavy hydrocarbons.

The CH₄ and H₂ in the second reaction zone product stream are recycledback to the first reaction zone. The additional hydrogen improves thecarbon efficiency of the methane to alkane process which results in areduced amount of fresh methane in the feed stream, a lower oxygen feedrequirement and essentially no CO₂ removal from the process, resultingin the highest natural gas efficiency. Some CO₂ is removed in an inertgas purge which is used to control N₂ and CH₄ concentration at thereactor inlet. But, a separate CO₂ removal system is not required.

The CH₄/alkanes ratio of Example 1 is 1.14; the O₂/alkanes ratio ofExample 1 is 1.05; and the carbon efficiency of Example 1 is 0.96.

Example 2

Example 2 is a simulation of the conversion of a carbon-containingstream to C₂ to C₅ hydrocarbons according to embodiments depicted inFIG. 2A. In particular, a feed stream comprising CH₄ and O₂ is fed to afirst reaction zone comprising an alkane production unit. The mass flowof the feed stream, based on the production of 1 lb. of ethylene, is2.093 lbs. CH₄ and 2.129 lbs. O₂.

The first reaction zone product stream comprises CO₂, H₂O, C₂H₆, C₃H₈,C₄H₁₀, and C₅H₁₂. The CO₂ and H₂O are separated from the remainingcomponents (i.e., C₂H₆, C₃H₈, C₄H₁₀, and C₅H₁₂) and discarded. The massflow of the first reaction zone product stream, based on the productionof 1 lb. of ethylene, is 0.003 lbs. CO₂, 2.360 lbs. H₂O, 0.588 lbs.C₂H₆, 0.984 lbs. C₃H₈, 0.304 lbs. C₄H₁₀, and 0.152 lbs. C₅H₁₂.

The C₂H₆, C₃H₈, C₄H₁₀, and C₅H₁₂ produced in the first reaction zone arefed to a second reaction zone. The C₂H₆, C₄H₁₀, and C₅H₁₂ produced inthe first reaction zone are fed along with a feed of additional freshethane to a conventional cracker, which produces C₂H₄, C₃H₆, C₄H₈, andC₅H₁₀ olefins. The C₃H₈ produced in the first reaction zone is fed to aconventional PDH reactor, which produces C₃H₆. The fresh ethane makes up17.5 wt % of the feed to the cracker. The mass flow of the fresh ethane,based on the production of 1 lb. of ethylene, is 0.430 lbs.

The outlet streams from the cracker and the PDH reactor are combinedinto a second reaction zone product stream comprising H₂, CH₄, C₂H₄,C₃H₆, C₄H₈, pygas, and other heavy hydrocarbons. The mass flow of thesecond reaction zone product stream, based on the production of 1 lb. ofethylene, is 0.1036 lbs. H₂, 0.2106 lbs. CH₄, 1.0000 lbs. C₂H₄, 0.9212lbs. C₃H₆, 0.0998 lbs. C₄H₈, 0.0863 lbs. pygas, and 0.0139 lbs. of otherheavy hydrocarbons.

The CH₄ and H₂ in the second reaction zone product stream are recycledback to the first reaction zone. The additional hydrogen improves thecarbon efficiency of the methane to alkane process which results in areduced amount of fresh methane in the feed stream, a lower oxygen feedrequirement and essentially no CO₂ removal from the process, resultingin the highest natural gas efficiency. Some CO₂ is removed in an inertgas purge which is used to control N₂ and CH₄ concentration at thereactor inlet. But, a separate CO₂ removal system is not required.

The CH₄/alkanes ratio of Example 2 is 1.14; the O₂/alkanes ratio ofExample 2 is 1.05; and the carbon efficiency of Example 2 is 0.96.

Example 3

Example 3 is a simulation of the conversion of a carbon-containingstream to C₂ to C₅ hydrocarbons according to embodiments depicted inFIG. 2B. In particular, a feed stream comprising CH₄ and O₂ is fed to afirst reaction zone comprising an alkane production unit. The mass flowof the feed stream, based on the production of 1 lb. of ethylene, is3.003 lbs. CH₄ and 3.051 lbs. O₂.

The first reaction zone product stream comprises H₂O, C₂H₆, C₃H₈, C₄H₁₀,and C₅H₁₂. There is no CO₂ in the first reaction zone product stream.The H₂O is separated from the remaining components (i.e., C₂H₆, C₃H₈,C₄H₁₀, and C₅H₁₂) and discarded. The mass flow of the first reactionzone product stream, based on the production of 1 lb. of ethylene, is3.386 lbs. H₂O, 0.843 lbs. C₂H₆, 1.410 lbs. C₃H₈, 0.436 lbs. C₄H₁₀, and0.218 lbs. C₅H₁₂.

The C₂H₆, C₃H₈, C₄H₁₀, and C₅H₁₂ produced in the first reaction zone arefed to a second reaction zone. The C₂H₆, C₄H₁₀, and C₅H₁₂ produced inthe first reaction zone are fed along to a conventional cracker, whichproduces C₂H₄, C₃H₆, C₄H₈, and C₅H₁₀ olefins. The C₃H₈ produced in thefirst reaction zone is fed along with a fresh feed of propane to aconventional PDH reactor, which produces C₃H₆. The fresh propane makesup 22 wt % of the feed to the PDH reactor. The mass flow of the freshpropane, based on the production of 1 lb. of ethylene, is 0.820 lbs.

The outlet streams from the cracker and the PDH reactor are combinedinto a second reaction zone product stream comprising H₂, CH₄, C₂H₄,C₃H₆, C₄H₈, pygas, and other heavy hydrocarbons. The mass flow of thesecond reaction zone product stream, based on the production of 1 lb. ofethylene, is 0.1490 lbs. H₂, 0.2971 lbs. CH₄, 1.0000 lbs. C₂H₄, 1.9900lbs. C₃H₆, 0.1317 lbs. C₄H₈, 0.1134 lbs. pygas, and 0.0176 lbs. of otherheavy hydrocarbons.

The CH₄ and H₂ in the second reaction zone product stream are recycledback to the first reaction zone. The additional hydrogen improves thecarbon efficiency of the methane to alkane process which results in areduced amount of fresh methane in the feed stream, a lower oxygen feedrequirement and no CO₂ removal from the process, resulting in thehighest natural gas efficiency.

The CH₄/alkanes ratio of Example 3 is 1.14; the O₂/alkanes ratio ofExample 3 is 1.05; and the carbon efficiency of Example 3 is 0.96.

Comparative Example 1

Comparative Example 1 is a simulation similar to Example 1, but no freshethane is fed to the cracker and hydrogen is not recycled back to thefirst reaction zone.

In particular, a feed stream comprising CH₄ and O₂ is fed to a firstreaction zone comprising an alkane production unit. The mass flow of thefeed stream, based on the production of 1 lb. of ethylene, is 2.47 lbs.CH₄ and 2.25 lbs. O₂.

The first reaction zone product stream comprises CO₂, H₂O, C₂H₆, C₃H₈,C₄H₁₀, and C₅H₁₂. The CO₂ and H₂O are separated from the remainingcomponents (i.e., C₂H₆, C₃H₈, C₄H₁₀, and C₅H₁₂) and discarded. The massflow of the first reaction zone product stream, based on the productionof 1 lb. of ethylene, is 0.688 lbs. CO₂, 1.922 lbs. H₂O, 0.560 lbs.C₂H₆, 0.936 lbs. C₃H₈, 0.290 lbs. C₄H₁₀, and 0.145 lbs. C₅H₁₂.

The C₂H₆, C₃H₈, C₄H₁₀, and C₅H₁₂ produced in the first reaction zone arefed to a second reaction zone comprising a conventional cracker, whichproduces C₂ to C₅ olefins.

The second reaction zone product stream comprises H₂, CH₄, C₂H₄, C₃H₆,C₄H₈, pygas, and other heavy hydrocarbons. The mass flow of the secondreaction zone product stream, based on the production of 1 lb. ofethylene, is 0.0513 lbs. H₂, 0.3677 lbs. CH₄, 1.0000 lbs. C₂H₄, 0.2445lbs. C₃H₆, 0.1160 lbs. C₄H₈, 0.1093 lbs. pygas, and 0.0170 lbs. of otherheavy hydrocarbons.

The CH₄/alkanes ratio of Comparative Example 1 is 1.28; the O₂/alkanesratio of Comparative Example 1 is 1.17; and the carbon efficiency ofComparative Example 1 is 0.85.

Comparative Example 2

Comparative Example 2 is a simulation similar to Example 2, but no freshethane is fed to the cracker and hydrogen is not recycled back to thefirst reaction zone.

In particular, a feed stream comprising CH₄ and O₂ is fed to a firstreaction zone comprising an alkane production unit. The mass flow of thefeed stream, based on the production of 1 lb. of ethylene, is 3.88 lbs.CH₄ and 3.54 lbs. O₂.

The first reaction zone product stream comprises CO₂, H₂O, C₂H₆, C₃H₈,C₄H₁₀, and C₅H₁₂. The CO₂ and H₂O are separated from the remainingcomponents (i.e., C₂H₆, C₃H₈, C₄H₁₀, and C₅H₁₂) and discarded. The massflow of the first reaction zone product stream, based on the productionof 1 lb. of ethylene, is 1.083 lbs. CO₂, 3.024 lbs. H₂O, 0.881 lbs.C₂H₆, 1.473 lbs. C₃H₈, 0.456 lbs. C₄H₁₀, and 0.228 lbs. C₅H₁₂.

The C₂H₆, C₃H₈, C₄H₁₀, and C₅H₁₂ produced in the first reaction zone arefed to a second reaction zone. The C₂H₆, C₄H₁₀, and C₅H₁₂ produced inthe first reaction zone are fed to a conventional cracker, whichproduces C₂H₄, C₃H₆, C₄H₈, and C₅H₁₀ olefins. The C₃H₈ produced in thefirst reaction zone is fed to a conventional PDH reactor, which producesC₃H₆.

The outlet streams from the cracker and the PDH reactor are combinedinto a second reaction zone product stream comprising H₂, CH₄, C₂H₄,C₃H₆, C₄H₈, pygas, and other heavy hydrocarbons. The mass flow of thesecond reaction zone product stream, based on the production of 1 lb. ofethylene, is 0.1188 lbs. H₂, 0.2666 lbs. CH₄, 1.0000 lbs. C₂H₄, 1.3659lbs. C₃H₆, 0.1308 lbs. C₄H₈, 0.1105 lbs. pygas, and 0.0182 lbs. of otherheavy hydrocarbons.

The CH₄/alkanes ratio of Comparative Example 2 is 1.28; the O₂/alkanesratio of Comparative Example 2 is 1.17; and the carbon efficiency ofComparative Example 2 is 0.85.

Comparative Example 3

Comparative Example 3 is a simulation similar to Example 1, but no freshethane is fed to the cracker.

A feed stream comprising CH₄ and O₂ is fed to a first reaction zonecomprising an alkane production unit. The mass flow of the feed stream,based on the production of 1 lb. of ethylene, is 1.965 lbs. CH₄ and2.142 lbs. O₂.

The first reaction zone product stream comprises CO₂, H₂O, C₂H₆, C₃H₈,C₄H₁₀, and C₅H₁₂. The CO₂ and H₂O are separated from the remainingcomponents (i.e., C₂H₆, C₃H₈, C₄H₁₀, and C₅H₁₂) and discarded. The massflow of the first reaction zone product stream, based on the productionof 1 lb. of ethylene, is 0.353 lbs. CO₂, 2.081 lbs. H₂O, 0.560 lbs.C₂H₆, 0.936 lbs. C₃H₈, 0.290 lbs. C₄H₁₀, and 0.145 lbs. C₅H₁₂.

The C₂H₆, C₃H₈, C₄H₁₀, and C₅H₁₂ produced in the first reaction zone arefed to a second reaction zone comprising a conventional cracker, whichproduces C₂ to C₅ olefins.

The second reaction zone product stream comprises H₂, CH₄, C₂H₄, C₃H₆,C₄H₈, pygas, and other heavy hydrocarbons. The mass flow of the secondreaction zone product stream, based on the production of 1 lb. ofethylene, is 0.0513 lbs. H₂, 0.3677 lbs. CH₄, 1.0000 lbs. C₂H₄, 0.2445lbs. C₃H₆, 0.1160 lbs. C₄H₈, 0.1093 lbs. pygas, and 0.0170 lbs. of otherheavy hydrocarbons.

The CH₄ and H₂ in the second reaction zone product stream are recycledback to the first reaction zone. However, a high amount of CO₂ is stillproduced in the first reaction zone. Accordingly, this process does notefficiently convert carbon in the feed stream to C₂ to C₅ hydrocarbons,and a separate CO₂ removal system is required.

The CH₄/alkanes ratio of Comparative Example 3 is 1.21; the O₂/alkanesratio of Comparative Example 3 is 1.11; and the carbon efficiency ofComparative Example 3 is 0.90.

Comparative Example 4

Comparative Example 4 is similar to Example 2, but no fresh ethane isfed to the cracker.

A feed stream comprising CH₄ and O₂ is fed to a first reaction zonecomprising an alkane production unit. The mass flow of the feed stream,based on the production of 1 lb. of ethylene, is 3.294 lbs. CH₄ and3.280 lbs. O₂.

The first reaction zone product stream comprises CO₂, H₂O, C₂H₆, C₃H₈,C₄H₁₀, and C₅H₁₂. The CO₂ and H₂O are separated from the remainingcomponents (i.e., C₂H₆, C₃H₈, C₄H₁₀, and C₅H₁₂) and discarded. The massflow of the first reaction zone product stream, based on the productionof 1 lb. of ethylene, is 0.283 lbs. CO₂, 3.402 lbs. H₂O, 0.881 lbs.C₂H₆, 1.473 lbs. C₃H₈, 0.456 lbs. C₄H₁₀, and 0.228 lbs. C₅H₁₂.

The C₂H₆, C₃H₈, C₄H₁₀, and C₅H₁₂ produced in the first reaction zone arefed to a second reaction zone. The C₂H₆, C₄H₁₀, and C₅H₁₂ produced inthe first reaction zone are fed to a conventional cracker, whichproduces C₂H₄, C₃H₆, C₄H₈, and C₅H₁₀ olefins. The C₃H₈ produced in thefirst reaction zone is fed to a conventional PDH reactor, which producesC₃H₆.

The outlet streams from the cracker and the PDH reactor are combinedinto a second reaction zone product stream comprising H₂, CH₄, C₂H₄,C₃H₆, C₄H₈, pygas, and other heavy hydrocarbons. The mass flow of thesecond reaction zone product stream, based on the production of 1 lb. ofethylene, is 0.1188 lbs. H₂, 0.2666 lbs. CH₄, 1.0000 lbs. C₂H₄, 1.3659lbs. C₃H₆, 0.1308 lbs. C₄H₈, 0.1105 lbs. pygas, and 0.0182 lbs. of otherheavy hydrocarbons.

The CH₄ and H₂ in the second reaction zone product stream are recycledback to the first reaction zone. However, a high amount of CO₂ is stillproduced in the first reaction zone. Accordingly, this process does notefficiently convert carbon in the feed stream to C₂ to C₅ hydrocarbons,and a separate CO₂ removal system is required.

The CH₄/alkanes ratio of Comparative Example 4 is 1.17; the O₂/alkanesratio of Comparative Example 4 is 1.08; and the carbon efficiency ofComparative Example 4 is 0.93.

Example 1 illustrates an improvement over Comparative Example 3, whileExamples 2 and 3 illustrate an improvement over Comparative Example 4,which is shown by the elimination of the CO₂ removal requirement fromthe first reaction zone, and by reducing the O₂/alkanes ratio. Example 1uses a small fresh ethane feed to the cracker, Example 2 uses a smallfresh ethane feed to the cracker, and Example 3 uses a small freshpropane feed to the PDH unit.

These examples illustrate several options for adding fresh ethane and/orfresh propane feed along with the feed produced from the first reactionzone so that the hydrogen produced from olefins production can berecycled back to the first reaction zone and reduce or eliminate the netremoval of CO₂ from the process. These examples illustrate variousoptions, but do not include all possible options.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the embodiments describedherein without departing from the spirit and scope of the claimedsubject matter. Thus it is intended that the specification cover themodifications and variations of the various embodiments described hereinprovided such modification and variations come within the scope of theappended claims and their equivalents.

The invention claimed is:
 1. A process for converting a feed streamcomprising carbon to C₂ to C₅ olefins, comprising: introducing a feedstream comprising methane and oxygen to a first reaction zone; reactingthe methane and oxygen in the first reaction zone to form a firstreaction zone product stream comprising a mixture of C₂ to C₅ alkanes;transporting the mixture of C₂ to C₅ alkanes to a second reaction zone;introducing a fresh stream of at least one of ethane and propane to thesecond reaction zone; converting the mixture of C₂ to C₅ alkanes to C₂to C₅ olefins in the second reaction zone; producing one or more productstreams in the second reaction zone, wherein a sum of the one or moreproduct streams comprises C₂ to C₅ olefins; and producing a recyclestream comprising hydrogen in the second reaction zone, wherein therecycle stream is transported directly from the second reaction zone tothe first reaction zone.
 2. The process of claim 1, wherein the secondreaction zone comprises a cracker.
 3. The process of claim 2, whereinintroducing a fresh stream of at least one of ethane and propane to thesecond reaction zone comprises introducing a fresh stream of ethane intothe cracker.
 4. The process of claim 2, wherein the second reaction zonecomprises a propane dehydrogenation reactor.
 5. The process of claim 4,wherein introducing a fresh stream of at least one of ethane and propaneto the second reaction zone comprises introducing propane into thepropane dehydrogenation reactor.
 6. The process of claim 5, wherein thesecond reaction zone comprises a cracker and introducing a fresh streamof at least one of ethane and propane to the second reaction zonecomprises introducing propane into the propane dehydrogenation reactorand introducing ethane to the cracker.
 7. The process of claim 1,wherein the recycle stream further comprises methane.
 8. The process ofclaim 1, wherein the first reaction zone product stream does notcomprise carbon dioxide.
 9. The process of claim 1, wherein the firstreaction zone comprises a hybrid catalyst.
 10. The process of claim 9,wherein the hybrid catalyst comprises a methanol synthesis component anda solid microporous acid component having 8-MR access.
 11. The processof claim 1, wherein a CH₄/alkanes ratio is less than 1.17.
 12. Theprocess of claim 1, wherein a CH₄/alkanes ratio is less than or equal to1.14.
 13. The process of claim 1, wherein an O₂/alkanes ratio is lessthan or equal to 1.10.
 14. The process of claim 1, wherein a carbonefficiency is greater than 0.93.
 15. The process of claim 1, wherein acarbon efficiency is greater than or equal to 0.96.
 16. The process ofclaim 1, wherein the first reaction zone comprises a reformer, a partialoxidation reactor, and a hybrid reactor, wherein the outlet stream ofthe reformer is introduced into the partial oxidation reactor, andwherein the outlet stream of the partial oxidation reactor is introducedto a hybrid reactor where the outlet stream from the partial oxidationreactor contacts a hybrid catalyst, and wherein the hybrid catalystconverts syngas into oxygenated hydrocarbons and the oxygenatedhydrocarbons into C₂ to C₅ alkanes.